The meshes that I make are based on the origin being at the origin of the original model and I take measurements from the mesh as shown in Fileviewer. The mesh requires a small textured object (I use a 10cm cube but it could be just one polygon if you wanted) positioned to be out of view. I can then add what missing attachment points and extra meshes such as seats, extra fittings, animated load, etc. that I want. I usually find that I need to usually fiddle with the position to get it right. Just for info for those that don't know, this only works for 2004 or later as you need the mesh table facility and you must alter the trainz build to 2.4 or higher. This also means for a pre 2004 config file it needs changing to the mesh table format.
Peter, ancient is as in having been around some time. As you will see my ID is 37096 (quite early). In fact I registered with Auran before Trainz appeared to get their MSTS DD40 model and as at that time I was an internet innocent (I retired from computer lecturing in 1991 just as Windows 3.1 arrived), this accounts for my rather stupid username. In fact I am 73 so a mere youngster.
